Cooperative Dynamic Positioning of Multiple Marine Offshore Vessels: A Modular Design

In this paper, a new cooperative control scheme is presented for the dynamic positioning of multiple offshore vessels, subject to the influence of persistent ocean disturbances induced by wind, waves, and ocean currents. The vessels are interconnected through an underlying directed network. Unlike the traditional dynamic positioning of individual marine surface vessels, cooperative dynamic positioning controllers are developed based on a modular design approach. Specifically, a predictor module is proposed for estimating the unknown ocean disturbances, which is able to achieve the disturbance estimation as fast as possible. Then, the controller module is designed based on a dynamic surface control technique. The input-to-state stability of the closed-loop network system is established via cascade theory. Furthermore, this result is extended to output feedback, where only the position-yaw information is available. Another predictor module is developed for estimating the unmeasured velocities, as well as unknown ocean disturbances. Then, the dynamic surface control technique is employed to devise the output feedback controller. The proposed designs result in decoupled estimate and control, and can achieve fast adaptation for both state and output feedbacks. Results of comparative studies are given to substantiate the efficacy of the proposed methods.